2. 12:3=20:5
6:3=4:2
56:7=72:9
81:9=36:4
14:2=49:7
80:8=100:10
6. a) 7*8+8:4=56+2=58
b) 24+5*(5:5-1)+25=24+5*(1-1)+25=24+5*0+25=24+25=49
c) 3*2:6*[20+(6:2-1)]-20=3*2:6*[20+(3-1)]-20=3*2:6*(20+2)-20=3*2:6*22-20=6:6*22-20=1*22-20=22-20=2
d) (20+12):(72-64):4=32:8:4=4:4=1
